With the development and progress of society, the usability of tools is required higher and higher. For example, for the use of a lawn mower, the known lawn mower usually uses only one battery pack to supply electricity. So, there is a problem that is the battery pack can't supply electricity for a long time, which can't satisfy the requirement of continuously cutting grass for a long time.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.